Aging Is Associated with reduced prostacyclin-mediated dilation in the human forearm

Aging is associated with reduced endothelial function. There is indirect evidence for reduced prostacyclin (PGI ₂)-mediated vasodilation with aging, but it is unknown whether this is because of reduced dilation to PGI ₂ or altered production. In addition, the contribution of endothelial NO to PGI ₂-mediated dilation is unknown. Using plethysmog-raphy to determine forearm blood flow, we studied the effect of PGI ₂ in 10 older (61 to 73 years) and 10 younger (19 to 45 years) subjects using 3 escalating intra-arterial doses of PGI ₂ (epoprostenol). PGI ₂ was also administered after NO synthase inhibition with A ^G-monomethyl-L-arginine acetate. The percent of change in forearm vascular conductance (mean±SEM) from baseline after PGI ₂ was significantly lower (P=0.002) in the aging individuals (52±11%, 164±23%, and 221±27% versus 115±20%, 249±19%, and 370±35%). In addition, the group-by-dose interaction was also significant (P=0.018). After NO synthase inhibition, the dose-response curve to PGI ₂ was blunted in the young subjects but unchanged in the older subjects; the difference between the groups was no longer significant. Our data suggest that the reduced dilator effects of PGI ₂ in older individuals are attributable to a reduction in the contribution of endothelial-derived NO versus alterations in the direct effects of PGI ₂ on vascular smooth muscle.